Smooth statistics for a point process on the unit circle with reflection-type interactions across the origin

Christophe Charlier

Published 2022-12-13Version 1

We study the point process \begin{align*} \frac{1}{Z_{n}}\prod_{1 \leq j < k \leq n} |e^{i\theta_{j}}+e^{i\theta_{k}}|^{\beta}\prod_{j=1}^{n} d\theta_{j}, \qquad \theta_{1},\ldots,\theta_{n} \in (-\pi,\pi], \quad \beta > 0, \end{align*} where $Z_{n}$ is the normalization constant. The feature of this process is that the points $e^{i\theta_{1}},\ldots,e^{i\theta_{n}}$ only interact with the image points $-e^{i\theta_{1}},\ldots,-e^{i\theta_{n}}$ obtained by reflection across the origin. We consider linear statistics of the form $\sum_{j=1}^{n}g(\theta_{j})$ as $n \to \infty$, where $g$ is H\"{o}lder continuous and $2\pi$-periodic. We prove that the leading order fluctuations around the mean are of order $n$ and of the form $\smash{\big(g(U)-\int_{-\pi}^{\pi}g(\theta) \frac{d\theta}{2\pi}}\big)n$, where $U \sim \mathrm{Uniform}(-\pi,\pi]$. We also conjecture that if $g \in C^{1,q}$, then the subleading fluctuations around the mean are of order $\sqrt{n}$ and of the form $\mathcal{N}_{\mathbb{R}}(0,4g'(U)^{2}/\beta)\sqrt{n}$, i.e. that the subleading fluctuations are given by a Gaussian random variable that itself has a random variance. We also derive large $n$ asymptotics for $Z_{n}$ (and some generalizations), up to and including the term of order $1$. Our proof uses techniques developed by McKay and Isaev [7, 5] to obtain asymptotics of related $n$-fold integrals.